1. Field of the Invention
The present invention relates to a marine engine for an outboard motor, and more particularly to a shift and throttle control mechanism for a marine engine.
2. Description of Related Art
Outboard motors recently have become equipped with four-cycle engines. The use of four-cycle engines in the power head of the outboard motor, however, raises some formidable challenges in regard to the engine layout and arrangement within the protective engine cowling.
For instance, in prior engine designs, the four-cycle engine commonly includes a large crankcase, as compared with two-cycle engines. A larger engine also results because a four-cycle engine requires an oil pan. As a result, prior outboard motor designs with four-cycle engines have struggled to provide sufficient space within the cowling in which to position many of the outboard motor components, including a shifting mechanism.
Prior shifting mechanisms often permit two separate control operators to couple to the shifting mechanism so as to control the shifting mechanism from two locations. One operator often is remotely positioned in the hull of the associated watercraft near the steering controls of the watercraft. The other operator usually comprises an integral part of the outboard motor and resides on a steering handle attached to a steering bracket of the outboard motor.
The shifting mechanism associated with an outboard motor employing a two-cycle engine usually includes a shift shaft to which shift control cables are attached. The points of attachment between the shift shaft and the shift control cables generally lie on the front side of the engine inside a lower tray of the outboard motor's cowling. The shift control cables extend from each operator to the shift shaft. Such cables, typically bowden-wire cables, usually include an inner cable wire that sides through an outer tubular casing. A fitting commonly connects an exposed end of the cable wire to the shift shaft, and a bracket fixes an end of the outer tubular casing within the lower tray.
Although desirable to fix the end of the cable tubular casing at a point near the shift shaft within the outboard motor's cowling, the size of the cowling's lower tray previously has not permitted it when used with four-cycle engines. A four-cycle engine usually occupies most of the space within the lower tray. Prior outboard motors thus have either enlarged the cowling or have not secured the end of the cable casing within the cowling lower tray. Both of these approaches though are less than satisfactory.
In addition, prior two-cycle outboard motors commonly employ a neutral safety mechanism that operates between the shifting mechanism and a throttle valve drive unit. The throttle valve drive unit is controlled by one or more operators via throttle control cables, and drives the actuation of one or more throttle valves on the engine. Such throttle valves, and thus the throttle valve drive unit, usually lie toward the forward end of the two-cycle engine. In this location, the throttle valve drive unit and the shifting shaft of the shifting mechanism reside near each other such that the neutral safety mechanism can regulate the throttle valve drive unit in accordance with the position of the shifting mechanism. The neutral safety mechanism prevents the engine from running at high speeds when the shifting mechanism establishes a neutral drive condition.
The adaptation of this safety mechanism to outboard motors employing four-cycle engines has been difficult, again because of space constraints caused by the larger engine. The arrangement of other engine components within the cowling has also posed problems. For instance, in a carbureted four-cycle engine, the carburetors usually lie at a generally central location on the side of the engine. The conventional neutral safety mechanism cannot be used with a carburetor so positioned because too long of a link is required to connect the throttle valves of the carburetors with the neutral safety mechanism. The link also typically must be bent at multiple locations in order to avoid other engine components. As a consequence, the manufacturing costs of the engine increase and the durability of the rod decreases.
A need therefore exists for a shift control mechanism for an outboard motor which allows a shift control cable from a remote operator to be fixed within the cowling of the outboard motor without requiring a larger cowling size. A need also exists for an improved neutral safety mechanism for a four-cycle engine.